Mechanical pot-seedling transplanting is an innovatively developed transplanting method that has the potential to replace mechanical carpet-seedling transplanting.  However, the initial pot-seedling transplanting machine lacked optimized density spacing and limited yield potential for japonica rice.  Therefore, ascertaining the optimized density by wide-narrow rows and the appropriate transplanting method for yield formation and grain quality of japonica rice is of great importance for high-quality rice production.  Field experiments were conducted using two japonica rice cultivars Nanjing 9108 and Nanjing 5055 under three transplanting methods in 2016 and 2017: mechanical pot-seedling transplanting with wide-narrow row (K, average row spacing of 30 cm); equidistant row (D, 33 cm×12 cm); and mechanical carpet-seedling transplanting (T, 30 cm×12.4 cm).  In addition, five different density treatments were set in K (K1–K5, from 18.62×10⁴ to 28.49×10⁴ hills ha^–1).  The results showed that the highest yield was produced by a planting density of 26.88×10⁴ hills ha^–1 in mechanical pot-seedling transplanting with wide-narrow row with a greater number of total spikelets that resulted from significantly more panicles per area and slightly more grain number per panicle, as compared with equidistant row, and yield among density in wide-narrow row showed a parabolic trend.  Compared with mechanical carpet-seedling transplanting, the treatment of the highest yield increased yield significantly, which was mainly attributed to the larger sink size with improved filled-grain percentage and grain weight, higher harvest index, and increased total dry matter accumulation, especially the larger amount accumulated from heading stage to maturity stage.  With the density in wide-narrow row decreasing, processing quality, appearance quality, and nutrition quality were all improved, whereas amylose content and the taste value were decreased.  Compared with mechanical carpet-seedling transplanting, mechanical pot-seedling transplanting improved processing quality and nutrition quality, but decreased amylose content and deteriorated appearance quality.  These results suggested that mechanical pot-seedling transplanting with wide-narrow row coupling produced a suitable planting density of 26.88×10⁴ hills ha^–1 and may be an alternative approach to improving grain yield and quality for japonica rice.

Mechanical transplanting with carpet seedlings (MC) and mechanical direct seeding (MD) are newly developed planting methods, which increase in popularity and planted area each year. Knowing the difference for yield and rice quality under different planting methods is of great importance for the development of high quality and yield cultivation techniques under mechanical conditions. Therefore, three kinds of japonica rice including hybrid japonica rice, inbreed japonica rice, and soft rice were adopted as materials. And the differences in the quality of processing, appearance, cooking and eating quality, nutrition, and the rapid viscosity analyzer (RVA) profile were studied to reveal the effects of planting methods on yield and quality of different types of japonica rice. Results showed that the milled rice and head rice rates under MC was significantly higher than those under MD, and the processing quality of inbreed japonica rice was the most stable. Compared with MC, length/width ratio of rice under MD was significantly increased, and chalkiness rate, size, and degree were significantly decreased. The protein content under MD was lower than that under MC. MC showed higher peak viscosity and breakdown value than MD. The taste value was the greatest for soft rice, followed by inbreed japonica rice, and then by japonica hybrid rice, with no significant differences resulting from planting methods. Compared with MC, MD significantly improved the appearance quality, though processing quality and nutritional quality were decreased. And there was no significant difference in cooking and eating quality between MC and MD. Under different planting methods, the appearance quality of inbreed japonica rice changed the most and the processing quality was the most stable. The nutritional, cooking and eating quality of soft rice changed the least. Therefore, according to the different planting methods and market needs, selecting the appropriate rice varieties can reduce the risks in rice production and achieve good rice quality.